Custom pie menu: shift in my hotkeys toggles multiselection mode between vertex edge and faces, how to toggle off previous mode?
import bpy
from bpy.types import Menu

class VIEW3D_MT_PIE_select_mode(Menu):
    bl_label = "Select Mode"

    def draw(self, context):
        layout = self.layout
        pie = layout.menu_pie()
        o = pie.operator("mesh.select_mode", text="Vertex", icon='VERTEXSEL')
        o.type = 'VERT'
        o.use_extend=False
        o.use_expand=False
        o.action='ENABLE'
        o = pie.operator("mesh.select_mode", text="Edge", icon='EDGESEL')
        o.type = 'EDGE' 
        o.use_extend=False
        o.use_expand=False
        o.action='ENABLE'
        o = pie.operator("mesh.select_mode", text="Face", icon='FACESEL')
        o.type = 'FACE'
        o.use_extend=False
        o.use_expand=False
        o.action='ENABLE'
        o = pie.operator("mesh.select_all", text="Select All/None", icon='RESTRICT_SELECT_OFF')
        o.action = 'TOGGLE'

addon_keymaps = []

def registerKeymaps():
    wm = bpy.context.window_manager
    if wm.keyconfigs.addon:
        km = wm.keyconfigs.addon.keymaps.new(name='3D View', space_type='VIEW_3D')
        kmi = km.keymap_items.new('wm.call_menu_pie', 'LEFTMOUSE', 'CLICK_DRAG', shift=True, alt=False,ctrl=False)
        kmi.properties.name="VIEW3D_MT_PIE_select_mode"
        addon_keymaps.append((km, kmi))

def unregisterKeymaps():
    for km, kmi in addon_keymaps:
        km.keymap_items.remove(kmi)
    addon_keymaps.clear()


def register():
    bpy.utils.register_class(VIEW3D_MT_PIE_select_mode)
    registerKeymaps()

def unregister():
    unregisterKeymaps()
    bpy.utils.unregister_class(VIEW3D_MT_PIE_select_mode)

if __name__ == "__main__":
    register()

    #bpy.ops.wm.call_menu_pie(name="VIEW3D_MT_PIE_select_mode")


This would work. But I strongly recommend not to use this since it will mess things up a lot. Shift + Left Click is used a lot in the keymap and it's not a good idea to replace it. It will make things inconsistent and I think you will likely regret it later if you get used to it doing something else in the viewport. Keys 1, 2 and 3 for mode selection are not that difficult to get used to, you should just suffer for a few days and get over it.